Rapport SGC 198 Bio-Propane from glycerol for biogas addition

1 IntroductionIn Sweden today there are large quantities of bio-methane produced via fermentation of differentwaste products e.g. manure, municipal waste, stover, etc. In Sweden 330 GWh wasused for heating purposes and 40 GWh for electricity production in 2005 (1), while 0.23 TWhwas used in the transport sector in 2006 (2). The produced bio-methane is in many casescleaned, upgraded and transferred to the natural gas grid. However, the bio-methane produceddoes not, even after upgrading, have the same heating value and wobbe index as the naturalgas. The first causes problems concerning metering and billing and the latter is a potentialproblem to certain groups of equipment. To circumvent this problem in the Swedish context,where Danish gas from the North Sea is mainly used, propane is added to the biogas before itenters the natural gas grid. Currently the added propane is of fossil origin (3) and shouldtherefore be replaced by propane or another gaseous, higher hydrocarbon from a renewablesource.As an alternative source of propane this report aims at investigating the possibilities of producingbio-propane from bio-glycerol. During the production of biodiesel via transestrificationfrom triglycerides, large quantities of glycerol are produced as by-product. Forevery 10 kg of biodiesel produced, 1 kg of glycerol is formed. The significant worldwide increasein biodiesel production has resulted in a glut on the glycerol market, with decreasingglycerol prices as a result. Glycerol has traditionally been a high-value chemical used in thefood and cosmetic industry, but has over the last few years decreased in price from about7 SEK/kg to less than 0.3 SEK/kg (4). This, in combination with increased feedstock cost, hasbasically undermined the profitability of any biodiesel operation. It has however created anentirely new research area, glycerol upgrading to high value chemicals.Besides biogas the produced propane, or propane equivalent, can be envisioned to fulfil otherpurposes than the biogas application intended. One such alternative use would be as a “green”component in LPG, making it possible to substitute parts of the LPG used to a low carbonfootprint LPG.BioFuel-Solution i Malmö AB have since the beginning of 2007 performed research withinthe field of glycerol conversion, mainly focused towards other alcohols. This research has todate resulted in 2 US patent applications, in association with an American biodiesel producer,and another 2 patent drafts within the field.1.1 BackgroundThe area of glycerol research has dramatically developed over the last 5-10 years, from thesynthesis of glycerol to the use of glycerol as a starting point for different synthesis. It is generallyaccepted that the primary source of renewable organic fuels, chemicals and materialswill be plant derived biomass (5) (6) (7) (8). But only 3% of the chemicals produced in theUS was biomass derived in 2004 (9). However, the US department of Energy (US DoE) aimat increasing the fraction of renewable chemicals to 17% by 2020 and 47% by 2050. Toachieve this, the US DoE has identified 12 chemicals to be used as building blocks for highvalue chemicals (10); glycerol is one of these and is readily available due to its productionwithin the biodiesel industry (11).The end-products most often mentioned in the glycerol context are ethylene- and1,2-propylene glycol and lactic acid. The first two chemicals are industrially important for themanufacturing of polymers, cooling fluids, food and cosmetics. Lactic acid is an importantfood industry chemical and the basis for producing poly-lactic acid (PLA). The demand of1